The invention pertains to alignment methods and alignment fiducials for the manufacture of circuits, integrated circuits, and circuit assemblies.
The miniaturization of electronic circuits and circuit assemblies has increased the performance of electronic systems while reducing both system costs and system size. Miniaturization has been enabled by the development of fabrication methods for small circuit features as well as circuit assembly methods that permit close component placement. In addition, multilayer substrates have been developed that permit more compact interconnection of circuit components.
Many of the benefits of miniaturization are lost if fabrication yields or fabrication throughput decline significantly because of miniaturization. One problem that successful fabrication methods must solve is that of carrying out a sequence of independent operations on a circuit or a substrate in such a way that these independent operations are properly aligned with the circuit or circuit substrate, and are aligned with each other. For example, circuit elements mounted to a substrate in successive steps must be aligned with corresponding mounting pads on the substrate. Protective coatings must be dispensed onto components that are to be encapsulated (xe2x80x9cpottedxe2x80x9d) with a coating material without dispensing the coating material in areas that are to remain uncoated.
In one fabrication method, multiple circuits or circuit assemblies are fabricated on a single substrate to improve throughput and reduce manufacturing costs. When fabrication is complete, individual circuits or circuit assemblies are obtained by cutting the substrate. In order to cut the substrate without damaging individual circuits, a pattern can be transferred to the substrate and used to define cut lines. However, if the pattern that defines the cut lines is not accurately transferred to the substrate, the cut lines are not properly placed on the substrate and individual circuits can be damaged by cutting along such improperly placed cut lines. For example, in one method of defining cut lines, patterns defining the cut lines are formed on the substrate using an etching process. If the etching process removes too little or too much material, then the transferred pattern will not accurately place the cut lines.
For these reasons, improved alignment methods, apparatus, and alignment patterns are needed for the fabrication of circuits and circuit assemblies.
A mask for transferring patterns to a substrate includes a fiducial pattern that includes a first set and a second set of complementary features with each set typically including plural features. The sets of features may comprise respective first and second pairs of features. The first and second sets of features may define a common axis that is equidistant from the complementary features of both sets. This fiducial pattern is transferred from the mask to a substrate such as by using a photolithographic process such as contact or projection printing, or a charged-particle-beam lithographic process. According to a representative embodiment, the common axis is a distance d1 from each of the complementary features of the first set or pair, and a distance d2 from each of the complementary features of the second set or pair. In further embodiments, the distance d2 is an integer multiple of the distance d1. The complementary features of the fiducial pattern can be any of various pattern features, including edges and ends of lines.
Circuits are fabricated using this mask by transferring the fiducial pattern to a circuit substrate and using the transferred fiducial pattern (referred to herein as a xe2x80x9cfiducialxe2x80x9d) to define an axis or other positional reference on the circuit substrate. The axis or other positional reference can be used in assembly or process steps, by defining an axis or axes along which the substrate is cut or otherwise divided, or defining a location at which components are inserted or other assembly operation is performed.
Substrates for circuits or circuit assemblies may include a fiducial that is defined by an etch process. The fiducial includes an etch compensation pattern that permits accurate determination of a substrate axis or location even if the etch process that defines the fiducial exhibits some process variation or error such as under- or over-etching. The fiducial includes an etch compensation portion that may define pairs of features such that each pair of features is equidistant from a common axis, but at different distances from the common axis. The common axis can be located by identifying the pair of features that are more nearly aligned, and defining the common axis with respect to this pair of features. In a representative embodiment, the pattern features are edges or ends of lines.
Etch gauges for determining an etch amount include a first pair and a second pair of features wherein the features of the first pair and of the second pair are equidistant from an axis.
A computer readable medium includes computer executable instructions for producing fiducial patterns on a mask or for directly writing such patterns on a substrate.
A method of aligning a substrate is provided that includes a step of defining a fiducial on the substrate, the fiducial including two or more sets of complementary features, each set of which may comprise respective feature pairs that define a first common axis. In a subsequent step, either the pair of features closer to the first common axis is selected and the first common axis is located as a line equidistant from the selected pair of features. In further embodiments, a line along which the substrate is cut is defined as a line parallel to the first common axis, and, in some examples, offset from the first common axis. In further embodiments, the method of aligning a substrate includes providing two or more pairs of complementary features that define a second common axis that intersects the first common axis.
In additional embodiments, a method of singulation is provided in which a substrate is provided with a fiducial that includes at two or more sets or pairs of complementary edges, line ends, or other features that define a common axis. The common axis is located as a line midway between corresponding feature pairs.
Fiducials are provided for defining cut lines singulation of a circuit substrate into multiple individual circuits. The fiducials include a first linear portion that has two or more sets or pairs of complementary edges that are placed symmetrically with respect to a first axis. Edges of the two pairs are placed a different distances from the first axis. The fiducials also include a second linear portion that has two or more pairs of complementary edges that are symmetrically placed with respect and at different distances from a second axis. The first axis and the second axis can be parallel or intersect.
These and other features and advantages of the invention are set forth below with reference to the accompanying drawings.